在 c 中使用 unistd.h 在 MAC OSX 上写入串行端口时出现问题
我正在尝试使用 c 中的 unistd.h Linux 函数写入 MAC OSX 上的蓝牙设备。 我连接良好并成功写入前几个字节。 当我尝试向其写入其他命令时(每 15 毫秒就会向写入缓冲区添加一些字节),即使 write() 函数返回 1(写入成功),我也看不到任何结果。
如果您开始一次写入,但在您尝试开始另一次写入时它尚未完成(因为它是非阻塞的),那么这可能会搞砸初始写入吗? (如果是这样,有什么方法可以检查写入是否已完成?)这是我能想到的唯一的事情,因为写入发生得相当频繁,并且前两个已成功发送。
qwbyte() 只是将一个字节添加到输出数组并增加其长度
打开端口函数:
BAMid = -1;
struct termios options;
struct termios originalTTYAttrs;
// Open the serial port read/write, nonblocking, with no controlling terminal, and don't wait for a connection.
BAMid = open(strPath, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (BAMid == -1)
{
printf("Error opening serial port %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// Issue TIOCEXCL ioctl to prevent additional opens except by root-owned processes.
if (ioctl(BAMid, TIOCEXCL) == -1)
{
printf("Error setting TIOCEXCL on %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// Get the current options and save them so we can restore the default settings later.
if (tcgetattr(BAMid, &originalTTYAttrs) == -1)
{
printf("Error getting tty attributes %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// The serial port attributes such as timeouts and baud rate are set by modifying the termios
// structure and then calling tcsetattr() to cause the changes to take effect. Note that the
// changes will not become effective without the tcsetattr() call.
options = originalTTYAttrs;
// Set raw input (non-canonical) mode, with reads blocking until either a single character
// has been received or a one second timeout expires. [should be moot since we are leaving it as nonblocking]
cfmakeraw(&options);
options.c_cc[VMIN] = 1;
options.c_cc[VTIME] = 10;
cfsetspeed(&options, B57600); // Set 57600 baud
options.c_cflag |= CS8; // Use 8 bit words
// Cause the new options to take effect immediately.
if (tcsetattr(BAMid, TCSANOW, &options) == -1)
{
printf("Error setting tty attributes %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
//flush old transmissions
if (tcflush(BAMid,TCIOFLUSH) == -1) {
printf("Error flushing BAM serial port - %s(%d).\n",
strerror(errno), errno);
}
oBufLength = 0;
// Ask it to start
if (! qwbyte(CmdStart) ) {
goto error;
}
if (! qwbyte(CmdFull) ) {
goto error;
}
//this transmit works
txbytes();
printf("success opening port!");
return -1;
// Failure path
error:
if (BAMid != -1) {
close(BAMid);
}
printf("returning an error--%d",errno);
return errno;
}
写入函数 (txbytes):
int i, bufSize, numBytes;
if(oBufLength != 0) { //if the output array isn't empty
//duplicating the output array and its size so it can
//be overwritten while this write is occuring
printf("about to transmit: ");
for(i = 0; i < oBufLength; i++) {
printf(" %u",oBuf[i]);
tempBuf[i] = oBuf[i];
}
printf("\n");
bufSize = oBufLength;
oBufLength = 0;
numBytes = write(BAMid, &tempBuf, bufSize);
printf("bytes written = %d\n",numBytes);
if (numBytes == -1) {
printf("Error writing to port - %s(%d).\n", strerror(errno), errno);
}
return (numBytes > 0);
}
else {
return 0;
}
I am trying to write to a bluetooth device on MAC OSX using the unistd.h Linux functions in c. I am connecting fine and writing the first few bytes with success. When I try to write other commands to it (there are bytes added to the write buffer every 15ms), I don't see any results even though the write() function returns 1 (write success).
If you start a write and it doesn't finish by the time you try to start another write (since it is non-blocking), could that possibly screw up the initial write? (If so, is there any way to check if a write has completed?) That is the only thing I can think of since the writes are occurring fairly frequently and the first two are successfully sent.
qwbyte() simply adds a byte to the output array and increments its length
The open port function:
BAMid = -1;
struct termios options;
struct termios originalTTYAttrs;
// Open the serial port read/write, nonblocking, with no controlling terminal, and don't wait for a connection.
BAMid = open(strPath, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (BAMid == -1)
{
printf("Error opening serial port %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// Issue TIOCEXCL ioctl to prevent additional opens except by root-owned processes.
if (ioctl(BAMid, TIOCEXCL) == -1)
{
printf("Error setting TIOCEXCL on %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// Get the current options and save them so we can restore the default settings later.
if (tcgetattr(BAMid, &originalTTYAttrs) == -1)
{
printf("Error getting tty attributes %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
// The serial port attributes such as timeouts and baud rate are set by modifying the termios
// structure and then calling tcsetattr() to cause the changes to take effect. Note that the
// changes will not become effective without the tcsetattr() call.
options = originalTTYAttrs;
// Set raw input (non-canonical) mode, with reads blocking until either a single character
// has been received or a one second timeout expires. [should be moot since we are leaving it as nonblocking]
cfmakeraw(&options);
options.c_cc[VMIN] = 1;
options.c_cc[VTIME] = 10;
cfsetspeed(&options, B57600); // Set 57600 baud
options.c_cflag |= CS8; // Use 8 bit words
// Cause the new options to take effect immediately.
if (tcsetattr(BAMid, TCSANOW, &options) == -1)
{
printf("Error setting tty attributes %s - %s(%d).\n",
strPath, strerror(errno), errno);
goto error;
}
//flush old transmissions
if (tcflush(BAMid,TCIOFLUSH) == -1) {
printf("Error flushing BAM serial port - %s(%d).\n",
strerror(errno), errno);
}
oBufLength = 0;
// Ask it to start
if (! qwbyte(CmdStart) ) {
goto error;
}
if (! qwbyte(CmdFull) ) {
goto error;
}
//this transmit works
txbytes();
printf("success opening port!");
return -1;
// Failure path
error:
if (BAMid != -1) {
close(BAMid);
}
printf("returning an error--%d",errno);
return errno;
}
The write function (txbytes):
int i, bufSize, numBytes;
if(oBufLength != 0) { //if the output array isn't empty
//duplicating the output array and its size so it can
//be overwritten while this write is occuring
printf("about to transmit: ");
for(i = 0; i < oBufLength; i++) {
printf(" %u",oBuf[i]);
tempBuf[i] = oBuf[i];
}
printf("\n");
bufSize = oBufLength;
oBufLength = 0;
numBytes = write(BAMid, &tempBuf, bufSize);
printf("bytes written = %d\n",numBytes);
if (numBytes == -1) {
printf("Error writing to port - %s(%d).\n", strerror(errno), errno);
}
return (numBytes > 0);
}
else {
return 0;
}
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非阻塞写入不会按照您期望的方式工作。
如果写入无法立即完成,则 write() 返回到您的代码 - 但它不会继续尝试在后台发送数据。 它所做的只是说“我现在无法写作 - 稍后再试”。 它通过返回 -1 来实现此目的,并将 errno 设置为 EAGAIN。
另外,请记住,成功时,write() 返回成功写入的字节数。 因此,如果当您请求写入 2 个字节时得到的返回值为 1,则意味着它仅部分成功,并且您需要再次调用 write() 来写入第二个字节。
基本上,如果您使用非阻塞 IO,您希望 txbytes() 函数在循环中调用 write() 直到缓冲区为空或返回 -1。 如果它返回-1,你需要检查 errno - 如果它是 EAGAIN,你将不得不在其他时间再次调用 write() ; 其他任何事情都可能是一个真正的错误。 像这样的事情:
请注意,无需复制缓冲区 - 因为 write() 不会与您的代码并行执行任何操作。 如果它说它已写入字节,则它不再需要您的缓冲区。 希望有帮助!
Non-blocking writes don't work how you're expecting them to.
If the write can't be completed immediately, write() returns to your code - but it doesn't keep trying to send the data in the background. All it does is say "I couldn't write at the moment - try again later". It does this by returning -1, with errno set to EAGAIN.
Also, remember that when successful, write() returns the number of bytes successfully written. So if you're getting a return value of 1 when you asked for 2 bytes to be written, that means it was only partially successful, and you need to call write() again some time for the second byte.
Basically, if you're using non-blocking IO, you want your txbytes() function to call write() in a loop until either your buffer is empty, or it returns -1. If it returned -1 you need to check errno - if it's EAGAIN, you'll have to call write() again some other time; anything else is probably a real error. Something like this:
Note that there's no need to duplicate the buffer - since write() doesn't do anything in parallel with your code. If it says its written the bytes, it doesn't need your buffer any more. Hope that helps!